1. Field of the Invention
The present invention relates generally to tieback systems for lateral well bores. More specifically, the invention relates to an improved apparatus used in a multilateral completion and a method of obtaining a multilateral completion. The apparatus and method are used to tieback or connect a lateral well that is drilled from a primary well, which may be vertical or deviated, by orienting a tieback assembly at the upper end of a liner in the lateral well bore adjacent a casing window using a key, key slot, no-go device, and bottom edge of the casing window to rotationally and longitudinally locate a tieback liner with respect to the casing window. The tieback liner is then coupled to a guide rail near the casing window. After the tieback liner is installed, the invention provides full bore access in the main well bore while supporting external loads on the tieback liner.
2. Description of Related Art
Lateral well bores are routinely used to more effectively and efficiently access hydrocarbon bearing formations. Typically, lateral well bores are drilled and accessed from a window that is formed in the casing of a central or primary well bore. The casing windows are often preformed at the surface of the well prior to installation of the casing. With the window formed, the lateral well bore is formed with a drill bit and drill string. Thereafter, the liner is run into the lateral well bore and “tied back” to the main well bore. This allows, for example, collection of hydrocarbons from the lateral well bore.
Lateral tieback systems are well known. Various types are in use, including hanger type systems that allow a lateral liner to be mechanically tied back to the main casing at the window opening with the tieback means extending at least partially into the primary well bore, thus reducing the diameter of the main casing. Flush mount systems currently available place the liner in the main casing then “chop off” the portion of the liner that extends up into the main casing.
Still other systems available utilize some form of liner hanger device placed in the main casing to connect the liner in the lateral well bore to the primary well bore. Some examples of lateral tieback systems are detailed in U.S. Pat. Nos. 5,944,108, 5,477,925, and 6,079,488, and those patents are incorporated herein by reference in their entirety. The “hook” liner hanger systems of the first two aforementioned patents utilize a pair of longitudinal lateral extensions (hooks) along the outside of a liner. The liner is inserted into a lateral well bore through a window formed in the main well bore casing until the hooks locate on the bottom edge of the window. The liner is then set in place to connect the lateral and primary well bores. However, in each of these systems, the liner extends significantly into the primary well bore and significantly restricts the internal diameter of the main casing.
Some hanger type systems do not adequately support external loads on the tieback liner, especially loads applied perpendicular to the liner, and do not prevent the liner from being pushed back into the main well bore casing.
There are other problems with currently available tieback systems. Systems that sever a section of the liner extending into the primary well bore require a milling process which is time consuming and expensive, always carries the risk of loss of the entire well bore during the installation process, and reduces the capacity to hold formation load. Existing liner hanger systems that use a permanent orientation device mounted in the main well bore to orient the liner window to the main casing take up space and may significantly reduce the internal diameters of both the lateral well bore liner as well as the main casing.
There is a need, therefore, for a tieback apparatus and method to complete a multilateral junction that will overcome the shortcomings of the prior art devices. There is a further need for a tieback apparatus that can be installed in new well bores that does not restrict the internal diameter of the primary well bore.
There is a further need, therefore, for a tieback system that more effectively facilitates the placement and hanging of a liner in a lateral well bore. There is a further need for a tieback system that can be mechanically oriented. There is yet a further need for a tieback system that can be rotationally and longitudinally located in a primary well bore using a key slot as a guide. There is yet a further need for a tieback system that can be placed in a well bore while minimizing the obstructions in the liner or the primary well bore casing after installation.
There is yet a further need for a tieback system that can maintain the position of the liner with respect to the main well bore casing as well as a need for a system that can support external loads applied to the liner.
There is yet a further need for a tieback system that can be cemented in a well bore and allows full casing access through the junction without restriction and which does not require any downhole milling of the liner with the accompanying generation of steel cuttings which can cause numerous problems like the sticking of drilling and completion tools.